Compressor motor time delay circuit



March 18, 1969 R. G. MCCREADY 3,434,028

COMPRESSOR MOTOR TIME DELAY CIRCUIT Filed July 14, 1966 /l4 EXPANSIONDEVICE l2 l6 f CONDENSER EVAPORATOR INVENTOR.

RAYMOND G. MC CREADY ATTORNEYS.

United States Patent Ofice 3,434,028 Patented Mar. 18, 1969 3,434,028COMPRESSOR MOTOR TIME DELAY CIRCUIT Raymond G. McCready, Marshalltown,Iowa, assignor to Lennox Industries, Inc., a corporation of Iowa FiledJuly 14, 1966, Ser. No. 565,219 US. Cl. 318-484 4 Claims Int. Cl. H02 1/04 ABSTRACT OF THE DISCLOSURE A compressor motor time-delay circuit forprotecting a refrigerant compressor against rapid cycling which includestime-delay means for maintaining a specified predetermined minimum timeperiod between starts of the compressor motor.

This invention relates to automatic control apparatus and moreparticularly, to a refrigerant compressor motor time delay circuit.

In operation of a refrigeration system utilizing a refrigerantcompressor, it is desirable to prevent short cycling of the compressormotor upon intermittent opening and closing of the controls for thecompressor. Many hermetic refrigerant compressors utilize a low startingtorque compressor motor. If an attempt is made torestart the compressorshortly after the previous shut-off, system pressure will not beequalized and the motor will be inadequate to operate the compressionmechanism. Without the time delay provided by the present invention, thecompressor motor locked rotor protection means could be called upon tofunction too frequently. After several cycles, motor temperatures mightincrease to a level that prevents reset of the overload safety devicefor extended periods of time, limiting the ability of the system tooperate as needed. Additionally, extremely rapid recycling of externalcontrol switches can occur, such as chattering of thermostat contactscaused by mounting on light walls subject to vibration. This type ofoperation can result in compressor motor and/or switching devicefailures because of extremely high transient currents. By preventingthis, the present invention provides improved protection to the motorand switching devices.

It is recognized that there have been previous attempts to utilize timermeans to prevent operation of the compressor in an on-oif manner whenswitches in the control circuit are opened and closed rapidly. Thermaltimers have heretofore been used and also mechanical switch timer meanshave been used. These systems, however, have not been altogetherreliable and are generally more complex and expensive than the presentconstruction.

An object of the present invention is to provide an improved compressormotor time delay arrangement.

Another object of this invention is to provide improved compressor motortime delay means for protecting a refrigerant compressor against rapidcycling that might be caused by chattering or rapid opening and closingof thermostat contacts, or by rapid voltage surges as a result oflightening. Other objects and advantages of the present invention willbecome apparent hereinafter.

The specific details of the invention and their mode of functioning willbe made most manifest and particularly pointed out in clear and preciseterms in conjunction with the accompanying drawing wherein:

The single figure illustrates schematically a refrigeration system andincludes schematically a wiring diagram of a presently preferred form ofcompressor motor time delay circuit.

Referring now to the drawing, there is illustrated a refrigerationsystem of conventional design that could utilize the present invention.The refrigeration system 10 includes a refrigerant compressor 11 whichmight be of the hermetic type wherein the motor and compressionmechanism are enclosed within a single hermetically sealed casing. Thecompressor in operation pumps high pressure vaporous refrigerant to thecondenser 12 through discharge line 13. In the condenser 12, thevaporous refrigerant is converted to the liquid phase. The condenser maybe air cooled or liquid cooled in a conventional manner. The liquidrefrigerant then flows from the condenser through an expansion deviceindicated generally at 14. Examples of suitable expansion devices arecapillary tubes or thermal expansion valves. Refrigerant passes from theexpansion device 14 to the evaporator 16, where the refrigerant mayevaporate and return to the vaporous phase. The refrigerant is returnedto the compressor through a suction conduit 17 connecting the evaporatorto the compressor.

In many applications the compressor motor is a low starting torque motorfor purposes of economy. In the event that the high side and low side ofthe refrigeration system are not balanced after shut-off of thecompressor. then the starting torque requirements will be excessive andthe compressor mot-or may stall.

Consider now the electrical circuit of the present invention forpreventing undesirable cycling of the compressor motor. The compressormotor 19 is supplied with power from a suitable source via lines T and TContactor coil 21 controls energization of the compressor motor throughopening and closing of contact 21a.

The contactor coil 21 is in a control circuit supplied with powerthrough leads L and L The leads L and L may be at a higher or lowervolt-age than lines T and T for example, a transformer may be used tochange the voltage at L and L although it may be taken directly from Tand T if desired.

Provided in the circuit is a thermostat or control switch indicatedgenerally at 20. The thermostat 20 closes in response to cooling demandand opens when the cooling demand is satisfied. In practice, a controlrelay actuated by a room thermostat provides the control switchcontacts.

Provided in series with the thermostat 20 is a protection switch 22,which, for example, may be a high pressure cut-out switch suitablyattached to the compressor or other part of the high pressure side ofthe refrigeration system which will open the electrical circuit if thecompressor head pressure exceeds a predetermined maximum. It will beunderstood that other desirable safety switches may be used in additionto the illustrated protection switch 22.

The compressor motor time delay circuit includes tim- .ing motor meanscomprising a timing motor 24, a cam 26 rotated by the motor and a pairof timing motor switches or contacts 24a and 24b actuated by the cam 26.

Connected in circuit with the timing motor 24 are a pair of relays. Thefirst relay is a single pole single throw type and includes a relay coil28 and a contact 28a in series therewith. The contact 28a is normallyopen, and when clos'ed is adapted to connect the relay coil 28 be tweenlines L and L so as to hold the relay coil energized.

The second relay is a single pole double throw type and includes relaycoil 30 and first and second contacts 30a and 30b. The contact 30a inline 32 is normally closed and the contact 30b in line 34 is normallyopen.

The contactor coil 21 is connected across lines 36 and 38. Contact 21ais adapted to open and close the circuit to the compressor motor 19,which is in a circuit across the lines T and T which are connected to asuitable source of power.

Considering now the electrical circuit at start-up, the thermostat 20 isnormally open until there is a demand for cooling. The contacts 24a and24b of the timing motor 24 are in the positions shown in dotted line.Upon closure of thermostat 20, 'a circuit is completed throughthermostat 20, protection switch 22, relay coil 28, contact 24b and line29 to line L Upon energization of coil 28 normally open contact 28a willbe closed and a holding circuit will be provided to maintain the coil 28energized.

The timing motor 24 is energized since a circuit is completed from L toL through the thermostat 20, the protection device 22, timing motor 24,contact 24a and normally closed contact 30a to L The circuits to thecontactor coil 21 and relay coil 30 are open since the switch 24b is inthe dotted line position and the contact 3012 in line 34 is open.

After a short interval of operation of timing motor 24, on the order of20 seconds, for example, cam 26 has rotated and switches 24a and 24bhave been moved to the solid line position indicated. Switch 24aswitches to the solid line position first, with switch 24b following bya short interval of time, on the order of two seconds. The timing motornow runs through switch 24a and lin 31.

Relay coil 30 and the compressor contactor coil 21 now are energizedthrough a circuit from lines L to L including contact 24b (which is inthe solid line position) and contact 28a. The coils 21 and 30 are heldenergized through the contact 30b in line 34, which was closed uponenergization of coil 30. Upon energization of the contactor coil 21,contactor coil contact 21a will close, thereby closing the circuitbetween lines T and T and permitting energization of the compressormotor 19.

Assuming that the demand for cooling has continued for a predeterminedtime period on the order of five minutes, thermostat 20 remains closedand the compressor motor 19 remains running. Relay contact 28a remainsclosed and contact 30b in line 34 remains closed. At the end of thepredetermined time cycle, the timing motor 24 is stopped as the camactuates switches 24a and 24b back to the dotted line position. Thetiming motor is stopped since the contact 30a in the line 32 has beenopened. The circuit will remain in this condition until the coolingdemand is satisfied and/ or a protective devic -is opened.

Assume an operating condition wherein after two or three minutes ofrunning time the thermostat 20 is opened. The relay coils 28 and 30 aswell as the contactor coil 21 are deenergized. Accordingly thecompressor motor 19 is stopped when contact 21a opens the circuit acrosslines T and T Also timing motor 24 will be stopped. In the event thatthe thermostat 20 recloses, the timing motor 24 will commence to runthrough contact 24a and line 31. However, the relay coils 28 and 30 andcontactor coil 21 will remain deenergized.

Should the thermostat 20 immediately reclose, the timer motor 24 will beenergized as indicated. However, the relays 28 and 30 and the contactorcoil 21 will remain deenergized. Thus the remainder of the time in thepredetermined time cycle will run out before the switches 24a and 24bcan be shifted back to the dotted line position illustrated.

In the event of an over-anticipated or misapplied thermostat that wouldproduce a cooling demand on-otf cycle of less duration than thepredetermined timing cycle, for example, a three minute on, three minuteoff cooling demand cycle, upon the first demand for cooling upon closureof thermostat 20, the timing motor 24 would be energized as indicatedabove. The contactor coil 21 would be energized after a delay of twentyseconds to energize the compressor motor for a period of two minutes andforty seconds in the illustrated embodiment of the invention. When thethermostat 20 opens at the end of three minutes, the compressor motor 19would be deenergized and the timing motor 24 would be deenergized. Thenwhen the thermostat 20 closed again calling for cooling, there would betwo minutes and twenty seconds of demand time left before switches 24aand 24b would be returned to the dotted line position by cam 26 actuatedby timin motor 24. The compressor motor 19 would remain off anothertwenty seconds before it could be restarted. The total time from startto restart then might be on the order of eight minutes and twentyseconds in the given example.

The compressor motor time delay circuit of the present invention may beprovided in a compact device that can be field wired to a refrigerationsystem with little difiiculty. The relay 28 is a simple single poledouble throw relay. The relay 30 is a simple single pole double throwrelay.

The novel compressor motor time delay circuit of the present inventionfunctions to provide a timed demand cycle. The circuit functions toprevent restart of the compressor motor for a minimum predeterminedtime, on the order of five minutes when the thermostat or safetyprotection switch is opened, so as to prevent undesirable rapidrecycling of the compressor motor, and thus prevent damag to thecompressor motor.

While I have described a presently preferred embodiment of theinvention, it will be understood that the invention is not limitedthereto, since it may be otherwise embodied within the scope of thefollowing claims.

I claim:

1. In a time-delay circuit for controlling operation of a refrigerantcompressor motor to permit equalization of pressures in therefrigeration system after shutdown and for minimizing undesirable rapidcycling of the compressor motor in operation, said compressor motorbeing adapted to be supplied from a source of electric power and powersupply means for the time-delay circuit, the improvement comprisingcontrol switch means for interrupting the power supply means, ontactorcoil means for controlling energization and deenergization of thecompressor motor time-delay means operative in response to closure ofthe control switch means for initiating a minimum predetermined timeperiod to prevent reenergization of the compressor motor for at leastsaid minimum predetermined time, said time-delay means including a firstrelay means, second relay means and timing motor means including firstand second cam-actuated switches, the contactor coil means including acontactor coil, the first relay means including first and secondcam-actuated switches, the first relay means including a first relaycoil and a normally open contact in series therewith, and the secondrelay means including a second relay coil and a first normally closedcontact and a second normally open contact, the second normally opencontact being in series with the second relay coil, the second normallyopen contact being in circuit with the contactor coil, whereby closureof the control switch means will energize the second relay coil, closingthe second normally open contact and completing a circuit through thecontactor coil to energize same and to energize the compressor motor andat the same time, the timing motor means will be actuated to initiatethe minimum predetermined time period, with subsequent opening of thecontrol switch means deenergizing the contactor coil to deenergize thecompressor motor, as well as the timing motor means, and with subsequentclosing of the control switch means being ineffectual to energize thecontactor coil and thereby energize the compressor motor until theminimum predeter' mined time period has elapsed.

2. A time delay circuit as in claim 1, wherein the timing motor meansincludes a timing motor and a cam operated from the timing motor foractuating each of said timing motor switches between a first positionand a second position, the first normally closed contact of the secondrelay means being in series with the timing motor when the first timingmotor switch is in the first position, the second normally open contactof the second relay means being parallel with the first relay coil andsecond cam actuated switch when said second switch is in said firstposition.

3. A time delay circuit as in claim 2, wherein the timing motor isenergized when the control switch means is closed and the first timingmotor switch is in the first position and which timing motor isdeenerized in the event that the control switch means is opened.

4. A time delay circuit as in claim 3 wherein the second cam actuatedswitch moves from the first position to the second position before thefirst cam-actuated switch and moves from the second position to thefirst position after the first cam-actuated switch.

References Cited UNITED STATES PATENTS 2,840,204 6/1958 Mathamel et a1.31 8-484 X 6 McNicol et al. Luber.

McGroth et al. 318-484 X Sudmeier 318-484 X Newman 318--484 X Kyle318848 X US. Cl. X.R.

